Method of making composite pavements



April 4, 1939-' J. G. FULLER METHOD OF MAKING COMPOSITE PAVEMENTS FiledAug. 28, 193e' NN S /fVl/E/w'o/e.I JHMES 6., FULLER,

Patented Apr. 4, 1939 UNITED STS GFFI'.

RIETI-IGI) 0F MAKING COMPOSITE PAVEMENTS corporation of IllinoisApplication August 28, 1936, Serial No. 98,313

4 Claims.

The present invention provides a novel and advantageous method ofsecuring a composite pavement formed of mineral aggregate coated with afusible protective coating and binding material. It is particularlyapplicable to asphaltic pavement formed of such mineral aggregate coatedwith biturnen.

Heretofore, efforts have been made with some degree of success to formsuch a paving material wherein the aggregate is distributedhomogeneously and each individual particle thereof is completely andevenly covered with the coating, and preferably is impregnated thereby.

The present invention comprises an improvement on such paving materialand the method of obtaining the same.

In brief, the invention comprises the selection of suitable mineralaggregate made up of varying sized particles; suitably mixing them sothat any increment of the mass thereof will have its proportional shareof each size; supplying to the thus mixed aggregate a coating of bitumenso that each individual particle is completely covered; and finallyforcing the bitumen into the pores and crevices of the aggregateparticles; such steps being carried out in the presence of and by asuitable medium that will not alter the physical properties, principallypenetrability and ductility, of the bitumen.

It is an object, therefore, of the invention to provide a unifiedprocess for making asphalt paving wherein the final product is entirelyhomogeneous in composition; and wherein the bitumen is produced,applied, mixed, and even caused to impregnato the aggregate withoutchanging the physical properties thereof.

It is a further object of the invention to provide a process involvingthe mixing of mineral aggregate with an oxidizable binder in thepresence of superheated steam.

It is a further object of the invention to provide a process for causingimpregnation of the mineral aggregate by the binder in such wise as toavoid oxidation of the latter.

It is a further object of the invention to provide the impregnationaforesaid by steam in such wise as to prevent emulsifying of themixture.

The drawing represents the cross-section of a mechanism suitable forcarrying out the process.

This mechanism comprises essentially a rotary drum sealed to preventescape of pressure and provided with means for introducing liquid or gaswithin the drum during its rotation.

This mechanism in detail comprises the drum I, this drum having acylindrical center portion (Cl. 10B-31) t and opposite end closures 3and 4 that are domed for structural reasons. At the centers of theclosures are suitable bearings 5 and 6 whereby the drum is supported onxed shafts I and 8, it being understood that suitable means to renderthe bearings airtight are provided. On the inner surface o-f thecylindrical portion 2 are angularly arranged blades 9. At one portionalso on the cylindrical portion 2 is provided an opening Iii having anairtight closure II held in place by suitable means, such as I2. Whenthe closure il is removed, the aggregate may be removed from orintroduced into the interior of the drum through the opening it.

A gear I3 is xed to the end closure 4 and meshes with a suitable drivinggear I4 driven from a source of power.

Extending through the shaft 8 is a pipe I5, the pipe communicating witha header I5 offset from the axis of the drum, as shown. Projectingdownwardly from the header i5 are spray nozzles I1, these spray nozzlesbeing suitably distributed along the header for purposes to bedescribed.

A pipe I8 extends through the bearing 'I and terminates in a T i3 towhich one end of the header' i6 is connected for rigidity and support. Aconnector 2@ plugged as at 2| holds the header EE to the T it butprevents communication therebetween. An outlet 22 is secured to thelower part of the T i9. The members 23 and 2,4 are fly wheels.

The process is practiced as follows:

A mineral aggregate is selected and, in the usual composition, itembodies due proportions of rocks and sand of different sizes. The massof aggregate is heated, and the undistributed proportions thereof arethen placed within the drum through the opening iB, and the closure IIis installed. Oi course, for iilling, the drum will be rotated from theposition shown in the drawing so that the opening is at the top side.With the closure tightly fixed in position the drum is rotated with theaggregate inside. The blades 9 cause the material to be shifted fromside to side and to roll over upon itself until it is completely andhomogeneously mixed. Stated differently, it is mixed until any incrementselected from the mass will have the same proportions of all the severalsizes of aggregate as any other increment. No loss of aggregate occursduring this mixing because of the fact that the drum is closed.

After the aggregate has thus been mixed a suiiicient length of time toeffect the proper distribution, the air in the drum may be dischargedthrough the pipe I3, preferably by the application ofV a non-oxidizinggas through the pipe l5. When the atmosphere within theV drum isnonoxidizing, the valves controlling the pipes l5 and I8 may be closed.As a suitable non-oxidizing gas, steam has the advantages of readyavailability and cheapness. The steam may be superheated, since in thatstate it will not condense on the aggregate or drum and foam in themixing, or form a lilm on the aggregate particles that will resistadhesion of the binder thereto.Y

The binder, usually a bitumen, asphaltic cement, is' then forced intothe header it through the pipe i5, and is sprayed into theV drum throughthe nozzles il. The p-ressure against the Vbinder is produced by steam,as will be noted. The effect of the spray nozzles, as shown, is toprovide a completely distributed and ne sheet of bitumen extendingtoward the wall of the cylinder. During this time, the cylinder isrotated and 'crevices of the aggregate particles.

the particles of aggregate are being exposed by the action of the drumand the blade 9 during such rotation. ince the spray is very fine, itimparts to each exposed particle of aggregate a thin coating of bitumen,and in so doin-g, by its force, displaces any gas films that surroundsuch particles. This coating is made more effective -by the fact thatthe nest particles of aggregate may be in suspension in the air of thedrum, as likewise may be line particles of bitumen so that they comeincontact with each of them. As the drum continues to rotate, eachparticle may be brought several times within the direct iield ofV thespraying bitumen until the particles are evenly covered by a completecoat. Owing to the fact that the bitumen is at this time liquid, andbecause it presents a very large surface area, oxidation could easilyoccur if the atmosphere surrounding were air. Either of these factorscontributes to the oxidation effect. The presence of the non-oxidizingatmosphere, as set forth, prevents the oxidation, the result of whichwould be to reduce the ductility and penetration of the binder 'in thenal pavement. Asl has been noted, it is desirable also to cause thebinder to impregnate the aggregate by penetration into the pores orcrevices of the aggregate particles. VThis may be effected by followingthe application of the binder by that of a non-oxidizing gas underpressure. As has been stated, the binder is forced into the drum byapplication of steam pressure. The quantity of binder is predeterminedby the design of the pavement, but should be of such quantity, at least,as will cover each particle of aggregate. The gas is applied to thissupply until it is all deposited into the drum, after which the steamitself is admitted through the nozzles until the pressure in the drum israised to such a point that the binder will be forced into the pores orNecessarily, this pressure will have to be evaluated according to thetemperature conditions of the material, and its physical properties.Certain representative values are given hereafter. Y

Where steam is used, it is desirably superheated, since then it will notcondense and form an emulsion with the coated aggregate, or preventproper adhesionrthereof. It is to be observed that the pressure of theiirst applied steam is not signicant, whereas in this impregnation step,itis.

During this step of impregnating, the aggregate is being agitated in themixer, with two results. Each particle of aggregate is being exposed tothe free action of the pressure medium,

and the particles are being rolled one upon another so that, if any hasexcess binder, it will be divided evenly among the others, and none willremain uncoated. Necessarily, during this mixing, the mass coolssomewhat, and the binder sets from its liquid state to one lessfree-flowing.

The pressure step is continued for a suitable length of time, until themass is fully mixed and distributed, and the desired impregnationeffected. The use of steam instead of air under pressure in this stepalone is of great significance, since tests have shown a preservation ofpenetrability and ductility of the asphalt as a result thereof.

At the end of the pressure step, the pipe I8v may be opened to exhaustthe pressure in the drum. The closure ii may be removed and the mass ofmaterial unloaded onto a truck. During the ensuing operationaincludinglaying, the exposure of the surfaces of the material is minimized, toreduce oxidation.

For illustrative purposes only, it may be suggested that the total timeof mixing including the dry mix may be about ve minutes, of which theiirst two are consumed in mixing the dry aggregate, approximately onefor applicationrof the binder, and the remaining' two for the final mix,including the pressure step, if used. Since the mixture is effectivelyperformed in this time, it will be evident to those skilled in the artthat the process is quicker than those formerly used. The temperature ofthe aggregate when loaded into the drum may be in the neighborhood of400 to 500 F. The steam may range from approximately 550 to 750 F. andfrom sixty to one hundred twenty-live pounds pressure. The

final mix as removed from the drum will ordinarily range approximately300 F.

The result of this use of the non-oxidizing gas, such as steam, in placeoi air, and the consequent reduction of oxidation, is that the ultimatecharacteristics of the bitulnen (particularly penetrability andductility) are substantially the same as prior to the time when thematerial was put in the mix; whereas, ordinarily, as compared with theconditions in the material before it is put in the mix, thesecharacteristics of the binder in the laid pavement may be reduced asmuch as fifty percent., or more. The impregnation obtained is just asgood as that oi air. Consequently, by employing this process, a road maybe Obtained having a much greater degree of flexibility and consequentresistance to Wear than has heretofore been secured.Y Greater adhesionbetween the aggregate particles results, in addition to the ner wearingqualities of the bitumen itself. rPhe employment of the process likewisegives uniform and homogeneous distribution of the aggregate particles intheir various sizes so that the base may properly be formed from thelarger particles with the smaller ones duly filling the interstices andall held tightly but resiliently in position by the one unoxidizedbituminous maintaining the steam in the superheated state,

has the further advantagethat, upon cooling, after the -mass is removedfrom the drum, the entrained air inevitably present to some extentWithin the pores and behind the coating, will contract so as to put anegative pressure behind the ngers of binder Within the pores and willtend to hold these fingers therein.

It is further to be understood that the invention is not limited to theparticular form of mixer shown, since clearly its principles areapplicable to other mechanisms.

What is claimed is:

1. In a method of preparing paving material, the steps of supplying anaggregate free of binder in a container to be mixed, discharging the airfrom said container and supplying a non-oxidizing gas therein and aboutthe aggregate in its stead, and adding bituminous binding material tosaid aggregate in said container in the presence of said non-oxidizingatmosphere.

2. In a method of preparing paving material, the steps of supplying anaggregate free of binder in a container to be mixed, causing saidaggregate to be heated, providing steam in said container to displacethe air therefrom and from about the aggregate, thereafter addingoxidizable binding material to the aggregate in the presence of thesteam, and mixing the binder and aggregate.

3. In a method of preparing paving material, the steps of supplying anaggregate free of binder in a container to be mixed, causing saidaggregate to be heated, supplying superheated steam in said container todisplace the air therefrom and from about the aggregate, adding abituminous binder to said aggregate in the presence of said steam, andmixing the binder and aggregate inthe presence of said steam.

4. In a process of preparing paving material, the steps of mixingaggregate free of binder in a movable closed container, dischargingsubstantially all of the air therefrom to supply a nonoxidizingatmosphere in the container and about the aggregate, thereafter sprayingan oxidizable binder into said container against the particles ofaggregate While they are moved in the container, and applying a pressureby said nonoxidizing atmosphere to said binder to cause the same topenetrate the pores of the aggregate.

JAMES G. FULLER.

